What do you mean an “Important Notice”? Do you mean a topic that is “sticky”, stuck to the top of the front page or top of a forum? If that’s what you mean, just create a post as keymaster, then after it’s posted, look at the bottom of the page, and you will see [Stick topic (to front)]. Click “Stick topic” to make it sticky and keep it at the top of the forum it’s in. Click “to front” to stick it to the top of the front page, which is useful if it applies to more than one forum.